Document how to build and change the documentation

[MrPowers]

Expected behavior: Setup instructions on how to build the documentation locally.

Actual behavior: User has to figure out how to build the documentation site locally (it's not hard, but would be easier with instructions).

Suggested change: explain how the user can build a virtual environment with the required dependencies and add contribution instructions on how to build the documentation site locally.

[github-actions]

Thank you for your interest in Apache Sedona! We appreciate you opening your first issue. Contributions like yours help make Apache Sedona better.